Accelerator combinations comprising thioperoxydiphosphate and bis (triazinyl) disulfides

ABSTRACT

Vulcanizable compositions and processes for vulcanizing rubber are disclosed comprising accelerator systems comprising mixtures of thioperoxydiphosphate and bis(triazinyl)disulfides.

United States Patent [1 1 Trivette, Jr. et a1.

1 1 ACCELERATOR COMBINATIONS COMPRISING THIOPEROXYDIPHOSPHATE AND HIS (TRIAZINYL) DISULFIDES [751 inventors: Chester D. Trivette, Jr.; John P.

Vanderkooi, both of Akron; Ralph A. Genetti, Copley, all of Ohio [731 Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Dec. 3, 1973 [211 App1. No: 421,125

[521 US. Cl 260/5; 260/795 B; 260/791 [511 Int. Cl. s. C08K 5/34; C081 3/24 [581 Field of Search .4 260/5 79], 79.5 B

[561 References Cited UNITED STATES PATENTS 3.419521 12/1968 Scott et a1 v 260/795 B 1 1 Nov. 11, 1975 3.619.211] 12/1971 Apotheker ct a1 360/5 3.635920 1/1972 Apotheker V r r r i, 260/795 B 3,642,727 2/1972 Ashworth et a1 260/795 B FOREIGN PATENTS OR APPLICATIONS worse: 8/1970 United Kingdom Primary [:.\wiiiner-John C. Bleutge Artur/zen Agent. or FirmRichard O. Zerbe [57] ABSTRACT Vuicunizuhlc compositions and processes for vulcanizing rubber are disclosed comprising accelerator systems comprising mixtures of thiopcroxydiphosphate and bis( triazinyl )disulfides.

8 Claims, N0 Drawings ACCELERATOR COMBINATIONS COMPRISING THIOPEROXYDIPHOSPHATE AND BIS (TRIAZINYL) DISULFIDES This invention relates to improved vulcanizable natural rubber compositions and to improved methods for vulcanization of natural rubber which comprises vulcanization systems comprising accelerator combinations comprising thiopcroxydiphosphate and bis( amino-striazinyl )disulfidcs.

BACKGROUND OF THE INVENTION Known accelerators belong to the class of organic disulfide accelerators, examples of different types of disulfide accelerators are thiazole disulfides, thiuram disulfides. thioperoxydiphosphates and diamino-s-triazinyl disulfides. The first two members of this series are potent accelerators alone and because of their powerful accelerating activity they are sometimes used with classes of other accelerators to activate the cure. Contrasted with the first two members of the series. the last two members exhibit considerably less accelerator activity, meaning. that they are slower curing and less efficient. Because of the lower cure rate exhibited by the latter types of disulfide accelerators. generally they are used in combination with one or both of the first mentioned disulfide accelerators or with other classes of accelerators to achieve adequate rates of cure. For exam ple. Scott and Williams. US. Pat. No. 3.419.52l issued Dec. 3l. 1968 discloses that the use of thioperoxydiphosphates in combination with other classes of accelerators reduces the cure time and the scorch tendency of the vulcanizable composition. Combinations of bis( diamino-s-triazinyl)disulfides. thiazole disulfides and thiuram disulfides are commercially available.

SUMMARY OF THE INVENTION It has now been discovered that sulfur vulcanizable diene rubber compositions the major proportion of the rubber being natural rubber having incorporated therein sulfur and a combination of thioperoxydiphosphate accelerator and bis(diamino-s-triazinyl)disulfide accelerator exhibits synergism in respect to higher modulus and tensile strength and higher heat stability compared to sulfur vulcanizates prepared from either accelerator in same amount or either accelerator mixed with other disulfide accelerators. It is indeed surprising that two relatively weaker disulfide accelerators when used together result in unexpectedly improved vulcanizate properties.

The synergistic accelerator combination of this invention comprises two components A and B. Component A comprises a known class of thioperoxydiphosphate accelerators such as described in the aforesaid US. Pat. No. 3.419.521; supra. and Component B comprises a known class of bis( amino-s-triazinyl )disulfides such as described in British Pat. No. l.20l,862. which disclosures are incorporated herein by reference. The amount of each component may vary from 10 parts by weight of one component and 90 parts by weight of the other component per I00 parts accelerator combination and synergism is observed. Sometimes. the combination comprises about 30 parts by weight of one component and about 70 parts by weight of the other component but more often combinations comprising equal amounts of each component are used. When disproportionate amounts of each component 2 are used. preferably thioperoxydiphosphate is the major component.

Known thioperoxydiphosphate accelerators may be characterized by the formula in which each R independently is alkyl. cycloalkyl. aryl or aralkyl. The number of carbon atoms of the R groups is a matter of choice but disulfides having ten carbon atoms or less in each R group are recommended since larger R groups tend to merely dilute the accelerator effect of the thiophosphoryl disulfide moiety which contributes substantially to the accelerating function. Thus. in a preferred group of thioperoxydiphosphates the number of carbon atoms in each R group does not exceed ten. Straight or branched alkyl radicals of l-lU carbon atoms represent a satisfactory subgroup with lower alkyl radicals of [-5 carbon atoms being preferred. lllustrative alkyl radicals are methyl. ethyl. propyl, isopropyl, n-butyl. isobutyl. sec-butyl. tert-butyl. pentyl. hexyl. l-methylhexyl. and octyl. Aralkyl radicals of 7-1U carbon atoms represent a suitable subgroup with benzyl being preferred. Illustrative examples of aralkyl radicals are a-methylbenzyl. 01.01- dimethylbenzyl. phenethyl. xylyl. phenylpropyl and phenylbutyl. Straight or branched cycloalkyl radicals of 5-10 carbon atoms represent a satisfactory subgroup with cyclohexyl being preferred. Illustrative examples of cycloalkyl radicals are cyclopentyl. lmethylcyclohexyl. 4-methylcyclohexyl. cycloheptyl. cyclooctyl and cyclodecyl. Aryl radicals of 6l0 carbon atoms represent a satisfactory subgroup with phenyl being preferred. Illustrative aryl examples are tolyl. 4-butylphenyl and napthyl.

Known bis(diamino-s-triazinyl )disulfide accelerators may be characterized by the formula in which R and R are hydrogen. alkyl. alkenyl. cycloalkyl. aralkyl or aryl or said radicals may be substituted by cyano. hydroxy or lower alkoxy; and R and R are alkyl. alkenyl. cycloalkyl, aralkyl or aryl or said radicals may be substituted by cyano. hydroxy or lower alkoxy. R and R and R and R respectively, together with the nitrogen atoms to which they are attached may form a heterocyclic ring. R, and R or R and R may be joined to each other through carbon forming a monoor bi-cyclic alkylene radical or may be joined to each other through oxygen or sulfur forming a single divalent radical attached to nitrogen comprising two alkylene radicals joined by oxygen or sulfur. The number of carbon atoms attached to the nitrogen is immaterial but lower molecular weight compounds are recommended. The range of carbon atoms of the representative subgroups of the alkyl. aralkyl. cycloalkyl and aryl 3 radicals and the illustrative examples of said radicals described in regard to the thioperoxydiphosphate accelerators are equally applicable to the triazinyl disulfide accelerators. Alkenyl radicals of 3-8 carbon atoms represent a satisfactory subgroup with allyl being preferred. Illustrative alkenyl radicals are Z-butenyl. 3- butenyl. isobutylene. l-pentenyl. 3-hexenyl and 2- methyl-lpcntenyl. Hydroxy substituted alkyl radicals of l-S carbon atoms are preferred. examples of which are hydroxymethyl. Z-hydroxyethyl. Z-hydroxypropyl. 3-hydroxy-1-propyl. 4-hydroxybutyl and S-hydroxypentyl. Alkoxy substituted alkyl radicals of l-S carbon atoms are preferred. etamples of which are methoxymethyl. Z-methoxyethyl. 3-methoxypropyl. Z-ethoxyethyl. and 4-methoxybutyl.

Hcterocyclicamino radicals of 4-8 carbon atoms are preferred. Examples of such radicals are pyrrolidinyl. 3.5-dimethylpyrrolidinyl. piperidino. 4-methylpipcridino. morpholino. thiomorpholino. lo-dimethylmorpholino. hexahydro-l H-azepin-l-yl and azabicyclot 3.1.2 )non-3-yl.

Examples of thioperoxydiphosphates are 0.0- dimethyl thioperosydiphosphate. ().U'-diethyl thioperoxydiphosphate. U,U-dipropyl thioperoxydiphosphate. U.U'-di n-butyl thioperoxydiphosphate. (),U'-

dicyclohexyl thiopcroxydiphosphate. O.U'-dibenzyl thioperoxydiphosphate. O.t)'-diphen vl thioperoxydiphosphate and U.U'-diisobutyl thioperoxydiphosphate.

Examples of bis(diamino-s-triazinyl)disulfides are bis( di-2.-l-dimethy lamino-striazin-o-yl )disulfide bis( di-2.4-diethylaminos-triazin-o-yl )disulfide bis( diL.-l-dipropylamino's-triazin-o-yl )disulfide bis( di- 2 .4 di isopropylamino-s-triazin-o-yl )disulfide bis( di-Z .4-diisobutylamino-s-triazin-o-yl )disulfide bis( di'2.4-methylamino-s-triazin-6yl )disulfide bis( di-2.4-ethylamino-s-triazin-6-yl )disulfide bis(di-Z.4-propylamino-s-triazin-o-yl)disulfide bis( di-2.4-isopropylaminos-triazin-o-yl )disulfide bis( di-2 .4-n-butylamino-s-triazin-o-yl )disulfide bis( 2-methylamino-4-dimethylamino-striazin-6-yl )dibis( Z-ethylaminoA-die thylamino-s-triazin-o-yl )disulbis( lpropylamino--l--dipropylamino-s-triazin-o-yl )di bis( 2-isopropylamino-4-diisopropylamino-s-triazin-(abis( l-methylamino-4-diethylamino-s-triazin-o-yl )disulbis( Z-methylamino-4-dipropylamino-s-triazin-o-yl )dibis( Z-ethylamino-4-dimethylamino-s triazin-6-yl )disulbis( lethylamino-4-dipropylamino-s-triazin-6-yl )disulbis( 2-cyclohexylamino-4-dicyclohexylamino-s-triazinbis( 2-benzylamino-4-dibenzylamino-s-triazin-(n-yl )dibis( 2-morpholino-4-ethylamino-s-triazin-G-yl )disulfide bis( 2 .4-dimo rpholino-s-triazin-6-yl )disulfide bis( 2.4dipiperidino-s-triazin-o-yl )disulfide and bis( Z-piperidino-4-ethylamino-s-triazin-6-yl disulfide.

The accelerator combinations of this invention are incorporated into the rubber by conventional techniques either by addition to an internal mixer. such as a Banbury mixer. or they may be added to the rubber on a mill. The accelerators may be added individually or may be added as a premixed blend. The fully compounded stocks are then heated to effect vulcanization. The amount of accelerator combination added varies depending upon the properties desired in the vulcanizate but generally the amount is between 0.2-6.0 parts by weight per 100 parts by weight of rubber with U.S2.0 parts by weight per 100 parts by weight of rubber being the amount commonly used.

The rubber stocks may include conventional compounding ingredients such as sulfur. carbon black, zinc oxide. reinforcing silica. stearic acid. extender oil. phenolic antidegradant. phenylenediamine antidegradant. tackifier. scorch inhibitor and bonding agent and may also include conventional accelerators. Sulfur. the vulcanizing agent. is added in the usual quantities with the amount varying depending upon the properties desired. generally the amount used is between about l4 parts per 100 parts rubber.

The synergistic effects of the accelerator combinations of this invention are realized in any sulfur vulcanizable diene rubber the major proportion of which is natural rubber. Examples of synthetic diene rubbers which are suitable for mixing with natural rubber include cis-4-polybutadiene, butyl rubber. ethylene-propylene terpolymers. polymers of l.3-butadiene. polymers of isoprene. copolymers of l.3-butadiene with other monomers. for example. styrene. acrylonitrile, isobutylene. and methylmethacrylate.

For the rubber stocks tested and described herein as illustrative of the invention. Mooney scorch times at the designated temperatures are determined by means of a Mooney plastometer. The time in minutes required for the Mooney reading to rise five points above the minimum viscosity is recorded. Longer times on the Mooney scorch test are desirable because this indicates greater processing safety. Cure characteristics are determined at the designated temperatures by means of the Monsanto Oscillating Disk Rheometer which is described by Decker. Wise and Guerry in Rubber World. December 1962. page 68. From the Rheometer data. the maximum torque. R max.. in Rheometer units is recorded. The increase in torque is a measure of the de gree of vulcanization and is proportional to the crosslink density. Heat stability is evaluated by reversion data using the Rheometer. The loss in torque after ten minutes heating at the indicated temperature beyond the time required to reach maximum torque is measured and recorded. Low torque loss indicates high heat stability. The time. r in minutes for a rise of two Rheometer units above the minimum reading, and the time. 1 required to obtain a torque of 90 percent of the maximum is recorded. The difference. r -t is a measure of the cure rate of the sample. Vulcanizates are prepared by press curing at the selected temperature for the time indicated by the Rheometer data to obtain optimum cure. The physical properties of the vulcanizates are measured by conventional methods.

DESCRlPTlON OF PREFERRED EMBODIMENTS the ingredients shown below in standard rubber mixing equipment. All parts are by weight. Santoflex l3 is N- l.3-dimethylbuty1)-N -phenyl-p-phenylenediamine. Vulcanizable compositions are prepared by adding sulfur. thioperoxydiphosphate accelerator and bis( diamino-s-triazinyl)-disu1fide accelerator. The properties of the vulcanizable compositions and of the vu1canizates are determined as previously described.

6 and 6 are stocks of this invention which demonstrate the surprising synergistic effect of the accelerator mixture. The data show that upon vulcanization the stocks containing the accelerator combination exhibit a significantly higher cross-link density as shown by the maximum torque and modulus values. In addition to the TABLE 1 Masterhalch Ingredient Parts by Weight Natural rubber 100.11 Zinc Oxide 3.0 Stearic acid 2.1) 1SAF carbon black 45.0 Hydrocarbon softener 5.11 Santofles 13 2.0

157.11 TOTAL 1 2 i 4 5 h Masterbatch 157.0 Sulfur 2.0 2.0 2.0 1 (J 1.0 l (J iLtf-diisopropyl thioperoxydiphosphate (1.5 11.25 l U (1 5 Bist 2-ethylamino- 4-dieth lamino-striuzino-yhdisulfide (1.5' 1.25 1.0 (I Mooney Scorch at 250F n 34.5 29.4 2611 4-3.] 38.4 32.1 Rheumeier data at 292F t -t 18.6 21.4 1-1.2 11.1 13.9 19.9 R max. 51 b3 79 4 no 83 Rheometer data at'328F R max. 4-1 56 61 -11 -19 b7 Rmersion. (in -lh. after min.) 3.8 3.9 1.5 1 4 (1.3 l) l Stress-Strain data at 292F Cure time. minutes it) 35 35 4U 65 30(1'1? modulus. psi l 1590 18811 10811 15611 2310 Ult. Tensile. psi 34110 37711 41411 3-1011 41211 4320 Stocks 1 and 4 are control stocks showing the accelerating activity of thioperoxydiphosphate alone at two different sulfur/accelerator ratios. Similarly. Stocks 2 and 5 are control stocks showing the accelerating activity of bis(diamino-s-triaziny1)disulfide alone. Stocks 3 Natural rubber C is-4p0lybutadiene rubber HAF black ISAF black Zinc oxide Stearic acid Santoflex l3 Hydrocarbon processing aids Silica Pine tar TOTAL Masterbatch A Bis( 2ethy1ztmino- 4 -diethylamino-striazin-o-y 1 ldisul- (LW-diisopropyl thioperoxydiphosphate Moone\ Scorch at 250F t minutes Rheometer data at 292F m- R. max 73 Rheometer data at 328F R. max

Re ersiom (in -1b.

after 10 min.) (1.9

Stress-Strain at 292F Cure time. minutes 55 300% modulus. psi 2350 .U Masterbatch B Sulfur 1 .43

Masterhatch A Masterbatch B TABLE ll-continued Masterbatch A Masterbatch B L'lt. tensile. psi 3780 3800 000 3050 3 l Il 3130 The data of Table ll indicate that the amount of both sulfur and accelerator can be substantially reduced by the use of the synergistic accelerator combinations of this invention and essentially the same state of cure or better is achieved.

Although the invention has been illustrated by typical examples. it is not limited thereto. Changes and modifications of the examples of the invention herein chosen for purposes of disclosure can be made which do not constitute departure from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. Sulfur vulcanizable diene rubber composition the major proportion of the rubber being natural rubber having incorporated therein sulfur and an accelerating amount of a synergistic accelerator combination of thioperoxydiphosphate accelerator of the formula in which R is alkyl of ll carbon atoms and bistdiamino-s-triazinyl )disulfide accelerator of the formula in which R, and R,, are hydrogen or the same as R and R R and R, independently are alkyl of l-l0 carbon atoms.

2. The composition of claim I in which the accelerator combination is in the amount of about 0.5-2.0 parts by weight per 100 parts by weight rubber and the amount of each thioperoxydiphosphate and his (diamino-s-triazinyl)disulfide is between about 30-70 parts per parts accelerator combination.

3. The composition of claim 2 in which R, and R are hydrogen or lower alkyl and R. R and R, are lower alkyl.

4. The composition of claim 3 in which each R is isopropyl. R, is hydrogen and R R, and R, are ethyl.

5. A process for vulcanizing rubber which comprises incorporating into sulfur vulcanizable diene rubber composition the major proportion of the rubber being natural rubber, sulfur and. in amount effective to accelcrate vulcanization. a synergistic accelerator combination of thioperoxydiphosphate accelerator of the formula in which R is alkyl of l carbon atoms and his (diamino-s-triazinyl) disulfide accelerator of the formula in which R, and R are hydrogen or the same as R and R,, R and R, independently are alkyl of l10 carbon atoms and heating to effect vulcanization.

6. The process of claim 5 in which the accelerator combination is incorporated in the amount of about 0.5-2.0 parts by weight per 100 parts by weight rubber and the amount of each thioperoxydiphosphate and his (diamino-s'triazinyl)disulfide is between about 30-70 parts per 100 parts accelerator combination.

7. The process of claim 6 in which R, and R are hydrogen or lower alkyl and R. R and R, are lower alkyl.

8. The process of claim 7 in which each R is isopropyl, R, is hydrogen and R R and R, are ethyl. 

1. SULFUR VULCANIZABLE DIENE RUBBER COMPOSITION THE MAJOR PROPORTION OF THE RUBBER BEING NATURAL RUBBER HAVING INCORPORATED THEREIN SULFUR AND AN ACCELERATING AMOUNT OF A SYNERGISTIC ACCELERATOR COMBINATION OF THIOPEROXYDIPHOSPHATE ACCELERATOR OF THE FORMULA
 2. The composition of claim 1 in which the accelerator combination is in the amount of about 0.5-2.0 parts by weight per 100 parts by weight rubber and the amount of each thioperoxydiphosphate and bis (diamino-s-triazinyl)disulfide is between about 30-70 parts per 100 parts accelerator combination.
 3. The composition of claim 2 in which R1 and R3 are hydrogen or lower alkyl and R, R2 and R4 are lower alkyl.
 4. The composition of claim 3 in which each R is isopropyl, R1 is hydrogen and R2R3 and R4 are ethyl.
 5. A process for vulcanizing rubber which comprises incorporating into sulfur vulcanizable diene rubber composition the major proportion of the rubber being natural rubber, sulfur and, in amount effective to accelerate vulcanization, a synergistic accelerator combination of thioperoxydiphosphate accelerator of the formula
 6. The process of claim 5 in which the accelerator combination is incorporated in the amount of about 0.5-2.0 parts by weight per 100 parts by weight rubber and the amount of each thioperoxydiphosphate and bis (diamino-s-triazinyl)disulfide is between about 30-70 parts per 100 parts accelerator combination.
 7. The process of claim 6 in which R1 and R3 are hydrogen or lower alkyl and R, R2 and R4 are lower alkyl.
 8. The process of claim 7 in which each R is isopropyl, R1 is hydrogen and R2, R3 and R4 are ethyl. 